Why are violins made by Antonio Stradivari, the 18th-century instrument maker, so dramatically better than anything built since? Instrument makers have patiently disassembled his violins and replicated the measurements exactly in new instruments. Physicists have used lab equipment to analyse the vibrational patterns of the front and back plates, which generate most of the sound, and had craftsmen carve new plates that faithfully reproduce the patterns. Chemists have cooked up recipes for the varnish that coats a violin's raw maple and spruce. Yet nothing duplicated the transcendently beautiful sounds of the violins made by Stradivari, and his Cremonese contemporaries Nicolo Amati and Giuseppe Guarneri.

But Joseph Nagyvary, 66, a biochemist at Texas A&M University, may have found the answer. Nagyvary, who also makes violins, violas and cellos, believes the chemists were closest to the truth. He says it is the varnish, together with the specially treated spruce, that makes Cremonese violins great. Neither had much to do with Stradivari. The local lumberman happened to supply him with the ideal wood, and the local apothecary with the perfect varnish. "Stradivari was a marvellous craftsman," Nagyvary observes, "but the magnificent sound of his instruments is a lucky accident."

Nagyvary's historical research yielded a crucial clue. According to an account by the aristocratic patron of Joannes Baptista Guadagnini, one of the last of the great Cremonese violin makers, it was important to use wood that had been dry-aged, with no extra treatment. Nagyvary was not convinced. "I think this may have been a deliberate deception," he says, "in order to keep anyone from copying the great masters and lowering the value of existing instruments."

He learned that the wood supplies were tightly controlled at the time by the government authorities in Venice: "If you just went out and cut wood from the forests, you could be thrown in jail." Instead, authorised woodcutters felled trees in the highlands and dumped logs into rivers, where they were carried downstream to their destination.

"The Venetian navy got the best wood for building its ships," Nagyvary says. "Only after bureaucrats had taken inventory and assessed taxes could wood merchants buy their supplies, and at this point, the wood had been sitting in water for weeks or even months." Sure enough, Nagyvary says, when he took electron micrographs of a handful of wood shavings from Cremonese instruments, residues of bacteria and fungi showed up, just as you'd expect in wood that's been sitting in water.

Using X-ray fluorescence spectroscopy, Nagyvary also found the slivers contained unusually large amounts of minerals, including potassium, sodium, aluminum, copper, iron and especially calcium and magnesium. Some might have been drawn from brackish water in Venetian lagoons, but the rest, Nagyvary decided, were probably the result of deliberately treating the wood with mineral solutions. This was not a preposterous notion: alchemy books (the chemistry texts of the day) had many recipes for mineral-rich wood preservatives used by furniture makers to protect chairs and tables against damage from insects and against rot.

Nagyvary began soaking chunks of spruce and maple in brews of preservative chemicals. He knew that some woodworkers soaked their lumber in solutions containing bovine dung and urine. So he put up a sign above a tub in a men's room in the biochemistry lab: "Please contribute generously to violin research."

He kept experimenting and in 1975 went to Cremona, where he talked a violin maker into building some instruments with his treated wood. This raised the question of the varnishing of the finished instruments. Physicists who study the vibrational qualities of wood say varnish as little as possible: varnish adds weight, keeping the fiddle from vibrating to its full potential. Nonsense, say many violin makers: varnish is essential to the beauty of a violin, and the secrets of the varnish are jealously guarded.

Many violin makers swear by oil-based varnishes; Nagyvary asserts that their instruments would be better off bare. "First the oil penetrates deep into the wood. Then it dries and becomes gummy. That dampens down the vibrations."

On the most pristine surviving Stradivarius violins, by contrast, the finish has a brittle, almost glassy look. "It's like a toffee apple," says Nagyvary. He believes that there are good reasons for this. A toffee apple's surface is hard and shiny because the molecules that make up its sugar coating link to form long, interlocked chains. If the Stradivarius varnish contained sugar or a polysaccharide, the molecules would have attached to one another and to the wood, stiffening it so it could vibrate more efficiently, the opposite of what happens with oil.

Nagyvary found support for his belief in 16th-century documents noting that wood finishes frequently contained powdered glass, porcelain or amber to add stiffness to the wood and make the finish glitter like a gem, and that fruit-tree extracts were widely used in wood varnishes.

"This makes perfect sense," he says. "The pectin creates beautiful polymers. It's what makes jellies jell." He picks up a beaker filled with a solution of gum from the guar plant. He adds borax, "in this mixture it acts as a cross-linker, weaving the chains of sugar molecules into a web". Suddenly, the liquid solidifies into a gelatinous mass. "We need an emulsifier, to make it fluid enough to work into the wood. I like to use ox-bile." He also adds quartz, amber, gypsum, coral, zinc and powdered ruby and sapphire. By the time he's ready to apply the mixture to the instruments he makes, it has the consistency of mayonnaise.

The test is in the playing, and Nagyvary claims that his lab tests show the sound patterns of his instruments match those of the best Stradivari. He and his colleagues have compiled an extensive database from which they can tell a great violin from a mediocre one. Their test is the pattern of frequencies they see on their computer screen.

"It turns out that the violins acknowledged to be great by expert listeners all look similar on the sound analyser," Nagyvary says. "And the pattern almost exactly reproduces that of the human voice."